These are the free QR Code readers for Android, Apple and Window phones. I use a QR Reader offered by Scan Me and I've used both (currently back on Android, I prefer the OS). I use QR Codes extensively throughout my marketing materials so it makes sense to offer the apps here for free.
Free QR Code Scanning Apps
Want the paid version (It's only £1.99 and offers more features) then visit the Scan.Me download page here here.